Construction of high humidity-stabilized ZnS-NiS composites by NiS-induced phase transition: demonstrated for sleep quality monitoring

Abstract

As a crucial electronic device in fields such as environmental monitoring, medical diagnosis, and smart homes, humidity sensors play a vital role in ensuring the efficient operation of relevant systems, with their accurate and rapid response performance being of paramount importance. Due to its distinctive electronic structure and hydrophilic properties, ZnS exhibits a rapid response to the adsorption and desorption of water molecules. This characteristic endows it with significant potential for applications in humidity-sensitive fields. However, most conventional synthesis methods yield cubic crystalline phase ZnS, which exhibits poor stability under high humidity conditions. The research in this work shows that introducing NiS induces a cubic to hexagonal phase transition in ZnS, effectively addressing poor stability of cubic ZnS. Meanwhile, the heterogeneous interface formed between ZnS and NiS generates a synergistic effect, optimizing the charge transfer path and efficiency within the material. When water molecules are adsorbed or desorbed, the charge transfer becomes smoother, making the material more sensitive to humidity changes. Finally, ZnS-NiS was coated on the interdigital electrodes to fabricate a flexible sensor. This humidity sensor demonstrates excellent long-term stability and a short response/recovery time (0.5 s/1.5 s), enabling precise monitoring of human breathing, including real-time tracking of breathing rate and sleep status (snoring, deep sleep, and light sleep). This work provides a new paradigm for designing stable and highly sensitive humidity sensors. Moreover, this synthetic method of this material holds significant reference value for the development of other gas sensing materials.